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Noradrenergic tuning, not simple rate effects, produces temperature-sensitivity of the respiratory network in bullfrogs

Vallejo, Mauricio
http://orcid.org/0000-0002-8922-6895
http://rave.ohiolink.edu/etdc/view?acc_num=wright1527181646566301

Abstract Details

2018, Master of Science (MS), Wright State University, Biological Sciences.
Animals match ventilation to metabolic and acid-base regulatory demands during changes in body temperature. Across vertebrates ventilation increases at warmer temperatures and decreases at cooler temperatures. At the organismal level this is attributed to metabolic feedback and/or alpha-stat pH regulation; however, the cellular mechanisms that produce ventilatory output in response to brain temperature changes remain unclear. To identify mechanisms underlying temperature-sensitivity of the respiratory control network, I used brainstem-spinal cord preparations producing spontaneously active, rhythmic motor output similar to breathing in vivo of adult bullfrogs Lithobates catesbeianus. In vitro brainstem-spinal cords were superfused with artificial cerebrospinal fluid (aCSF) equilibrated at 90% O2, 1.3% CO2, and balance N2. Whole nerve recordings from the trigeminal (V) and vagus (X) nerves were used for measuring respiratory-related activity. I applied temperature ramps from 20ºC to 15ºC and then to 25ºC; each step lasted 15 minutes. Bursting frequency was analyzed for the last 5 minutes of each step and then normalized to percent of baseline (20ºC). Consistent with in vivo and in vitro data (Bicego-Nahas and Branco, 1999; Morales and Hedrick, 2002), I demonstrate that the frequency of respiratory-related nerve activity is stable across high temperatures, but not lower temperatures (One-way ANOVA p<0.0002; burst frequency different at 15ºC compared to 20ºC and compared to 25ºC, but no difference between 20ºC and 25ºC; Tukey's Multiple Comparison post hoc test). The locus coeruleus (LC) is a nucleus of the respiratory network and is the main supplier of norepinephrine in the brain. LC neurons from bullfrogs are paradoxically activated by decreases in temperature (Santin et al., 2013) suggesting that firing frequencies inversely proportional to temperature may play a role in setting the respiratory frequency across temperatures. To identify the role of norepinephrine in generating the respiratory frequency, I applied the temperature protocol while blocking the main adrenergic receptors (AR). For blocking a1AR, preparations were superfused with aCSF containing prazosin and for blocking a2AR I used RX821002. I found that bursting stability at high temperatures is disrupted when a1AR are blocked (One-way ANOVA p<0.0001; burst frequency significantly lower at 15ºC compared to 20ºC and 25ºC, and significantly lower at 20ºC compared to 25ºC; Tukey's Multiple Comparison post hoc test). In contrast, stable pattern across warm temperatures was maintained while the inhibition of bursting at 15°C was lost when a2AR were blocked (One-way ANOVA p=0.025; Tukey's Multiple Comparison post hoc test showed no difference in burst frequency between 15ºC, 20ºC and 25ºC). These results imply that norepinephrine tuning through different receptors, rather than simple Q10 effects, plays a major role in generating the breathing frequency across temperatures to match metabolic demands and acid-base regulation requirements at those temperatures.
Lynn Hartzler, Ph.D. (Advisor)
Christopher Wyatt, Ph.D. (Committee Member)
David Goldstein, Ph.D. (Committee Member)
39 p.
Biology
Noradrenergic tuning; temperature-sensitivity; respiratory network; bullfrogs; ventilation; metabolic feedback; brainstem-spinal cord

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Citations

  • Vallejo, M. (2018). Noradrenergic tuning, not simple rate effects, produces temperature-sensitivity of the respiratory network in bullfrogs [Master's thesis, Wright State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=wright1527181646566301

    APA Style (7th edition)

  • Vallejo, Mauricio. Noradrenergic tuning, not simple rate effects, produces temperature-sensitivity of the respiratory network in bullfrogs. 2018. Wright State University, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=wright1527181646566301.

    MLA Style (8th edition)

  • Vallejo, Mauricio. "Noradrenergic tuning, not simple rate effects, produces temperature-sensitivity of the respiratory network in bullfrogs." Master's thesis, Wright State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=wright1527181646566301

    Chicago Manual of Style (17th edition)

wright1527181646566301
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This open access ETD is published by Wright State University and OhioLINK.